1. Field of the Invention
The present invention relates to butt resistance welding and, more particularly, to a flash-butt resistance welding process. The invention can be successfully utilized for welding thick-walled or large compact parts on machines for flash-butt resistance welding.
2. Description of the Prior Art
Known in the prior art is a flash-butt resistance welding process in which the first stage of the welding process includes heating of parts by the welding current. The parts are preheated by the resistance method involving intermittent current pulses. The current is interrupted either by opening of the welding circuit by reciprocating motion of one of the parts being welded or by periodic disconnection of the primary winding of the transformer from the power mains (UK Pat. No. 984,296, Cl.B23K, 1965). In this welding process the parts are periodically brought together to form steady contact between their touching surfaces then spread apart until the welding circuit is opened.
However, the known process fails to ensure uniform heating of parts throughout their section and a high quality of the welded joint.
Also known in the prior art is a flash welding process without preheating in which the motion speed of the parts being welded is periodically and momentarily raised (USSR Inventor's Certificate No. 226745, Cl.H05B, 1968). As this speed is increased, the number of elementary contacts between the flashed butt ends of the parts grows sharply while on reduction of this speed the number of contacts diminishes and stays at the previous level for some time. The changes of speed are corrected in such a way that after raising the current intensity to a certain value the speed begins to be reduced to the initial level thereby avoiding short circuits between the butt ends of parts. However, it proves practically impossible to avoid opening of the welding circuit on reduction of speed which causes pauses in the flashing process. This extends the welding time and, consequently, reduces the output of the welding machine.